A radar cross section (RCS) of an object is a measure of how visible the object is to radar, i.e., to what extent a radar signal is reflected by the object back toward a radar system. Low RCSs are desirable in many military contexts, such as stealth aircraft. Antennas, such as those used for communication, location finding (beacons) and radar systems, conventionally include metal elements, which have high RCSs.
Every antenna has one or more driven elements, i.e., elements that are directly connected to one or more feedlines. Some antennas also have one or more parasitic elements, i.e., elements that are not directly connected to feedlines, but that are coupled to the driven element(s) only by electric and magnetic fields. Parasitic elements include reflectors and directors. Conventional metal elements reflect radar signals. Thus, these elements have relatively large RCSs, making them vulnerable to detection by enemy radars.
Conventionally, the RCS of an antenna may be reduced by housing the antenna within a radome embedded with frequency selective surfaces (FSS). The FSSs are designed to pass electromagnetic radio frequency (RF) signals radiated by the antenna and signals intended to be received by the antenna, but the FSSs are designed to absorb, or at least reduce reflection of, signals from an enemy radar system. Multiple layers of FSS may be used in the radome to mitigate radar signals at multiple frequencies.
Such radomes are, however, large, massive and difficult to design. Such radomes detune the antennas housed within them, thereby often requiring matching networks at inputs of the antennas or redesigns of the antennas. Furthermore, such radomes alter radiation patterns of the antennas housed within them. Thus, radomes and the antennas they house often need to be co-designed to achieve desired characteristics of both the radomes and the antennas. Frequently, many iterations are required in the co-design process for an antenna and its radome. Furthermore, if an antenna is replaced with an antenna of a different design, its radome may also need to be replaced. Consequently, designing, building and maintaining these radomes and antennas to be housed within them is expensive, complex and time-consuming.